Test suite: escape regexp special characters when constructing the firewall log parsing regexp.

.. and pass -P to grep, since Ruby uses PCRE.

features/step_definitions/tor.rb

@@ -160,9 +160,11 @@ Then /^the firewall is configured to block all IPv6 traffic$/ do
 end
 
 def firewall_has_dropped_packet_to?(proto, host, port)
-  regex = "^Dropped outbound packet: .* DST=#{host} .* PROTO=#{proto} "
+  regex = "^Dropped outbound packet: .* "
+  regex += "DST=#{Regexp.escape(host)} .* "
+  regex += "PROTO=#{Regexp.escape(proto)} "
   regex += ".* DPT=#{port} " if port
-  $vm.execute("journalctl --dmesg --output=cat | grep -q '#{regex}'").success?
+  $vm.execute("journalctl --dmesg --output=cat | grep -qP '#{regex}'").success?
 end
 
 When /^I open an untorified (TCP|UDP|ICMP) connections to (\S*)(?: on port (\d+))? that is expected to fail$/ do |proto, host, port|